I have lots of hills in my area. The only suggestion I have is to work hard in a low, low gear on the trainer. My trainer has a band system on it which increases resistance (the Kreitler Wind Machine) so choosing the hardest gear, and using the lowest (harder) resistance on that band is as close to it as I can get in winter.

Unfortunately it's a different kind of riding than flats or gradual slopes. I can ride 100 miles of hills, but I will have MY *** handed to me if I try to ride 100 miles on the flats of Florida.

You push hard, til you think your legs will burn and there's nothing left, and then you rest. With some of my mountains here... that rest is sometimes a few miles of gliding along!